It is known to employ a pair of planetaries to provide differential drive respectively to a pair of output assemblies such as ground engaging wheels or a continuous belt or track. The planetaries may be arranged such that their respective sun gears are driven by a common drive member or shaft. The main drive source, typically a drive shaft propelled by an internal combustion engine, may be in mesh with a ring gear of one of the planetaries through multiple gear assemblies to provide directionality and gear reduction. Typically, the drive source includes a rotational axis perpendicularly located relative the rotational axis of a driven axle or output which is commonly referred to as a “cross-drive”. For example, U.S. Pat. No. 4,357,840 issued to Winzeler, having an issue date of Nov. 9, 1982 and U.S. Pat. No. 4,423,644 issued to Coutant, having an issue date of Jan. 3, 1984 which are assigned to the assignee of the present invention, show differential assemblies having a pair of planetary assemblies driven in a cross-drive orientation. In operation, the planetary assemblies are in continuous driving engagement through a common shaft.
However, electrically driven powertrain systems may provide additional advantages since the drive source has been integrated into the differential to desirably reduce losses caused by the cross-drive connection, in addition to providing a more compact powertrain assembly. Additionally, there are also significant cost benefits of such an integrated arrangement. For example, U.S. Pat. No. 5,620,387 issued to Janiszewski provides an electric motor driving an axle through multiple, stacked and interconnected assemblies including a two-speed reducer, a reduction planetary and a bevel-gear nest.
Moreover, differential assemblies, by nature, are configured to transfer torque substantially equally between the outputs. For example, on a ground-engaging machine the torque generated by the drive source is transported to the wheels. However, known differentials transmit torque to the wheels regardless of wheel speed and are thus prone to wheel slippage especially at low speeds. On construction machines such as a wheel loader, such wheel slippage is typical as the machine is maneuvered to fill its bucket, for example. If a wheel slips a portion of the traction may be lost corresponding to an inefficient operation. Such events are time consuming, and significantly increase the operational costs associated with increased fuel usage, increased machine maintenance and increased time to complete the required task.
Therefore, it is desired to provide an inexpensive and compact differential assembly which, when operated, exhibits a reduction in losses between the drive source and the final drive assemblies, and additionally does not include significantly expensive componentry. Further, it is desired to provide a differential which limits wheel slippage to increase efficiency and enhance maneuverability.